Controllable Screw Spindle Pump

ABSTRACT

A controllable screw spindle pump for the lubricating oil supply of an internal combustion engine comprises a pump housing ( 1 ), in which a throttle chamber ( 13 ) and a control chamber ( 14 ) are configured which are in contact with the lubricating oil to be conveyed; wherein the throttle chamber ( 13 ) is arranged between the pump inlet ( 10 ) and the spindle chamber ( 12 ), and the throttle chamber ( 13 ) comprises a throttle valve ( 3 ), by way of which a throughflow cross section of a conveying stream can be set; and the control chamber ( 14 ) comprises a hydraulic control valve ( 4 ) with a piston ( 40 ) which responds to a hydraulic control pressure (p 1,  p 2 ) in the control chamber ( 14 ), and the control chamber ( 14 ) is oriented parallel to the spindle chamber ( 12 ) in relation to an actuating travel of the piston ( 40 ); and a valve body ( 30 ) of the throttle valve ( 3 ) is coupled to the piston ( 40 ) of the hydraulic control valve ( 4 ).

The present invention relates to a controllable screw pump having compact dimensions which is suitable for supplying lubrication oil to combustion engines in vehicles, more particularly passenger cars.

In vehicles, vane pumps and geared pumps are generally used as oil pumps which are driven by a drive shaft of the combustion engine. Vane pumps and geared pumps are displacement pumps which have a small axial dimension and are also available as variants with a variable pump geometry. A variable geometry can change the delivery volume in relation to the shaft rotation, whereby in particular in relation to applications with rotational speeds which fluctuate greatly, such as when operating combustion engines in passenger cars, a delivery amount or oil pressure can be adapted.

After many years' optimisation, vane pumps achieve an overall degree of efficiency of approximately 70% in a favourable operating point. Within wide ranges of the rotational speed-pressure characteristic map, the overall degree of efficiently falls greatly, e.g. at high rotational speeds to merely 35%. Furthermore, the technical maturity of these types of pump does not allow the expectation of much room for further improvements in the degrees of efficiency.

In contrast, screw pumps operate with degrees of efficiency of 70% to 85% at the rotational speeds, pressures and volume flows with low-viscous lubrication oils which are typical for lubrication oil applications. Accordingly, further potential savings in fuel consumption and CO₂ emission could be achieved by using screw pumps.

The structure of screw pumps comprises no delicate elements or sliding fits, whereby, even with long intervals between maintenance operations, the type of pump is relatively insensitive to becoming contaminated with soot or metal abrasion in the lubrication oil. In addition, they have a high power density, whereby they can achieve high delivery pressures in relation to a supply of lubrication oil.

However, screw pumps are fixed displacement pumps, the displacement volume of which cannot be adjusted. Furthermore, the structure is of a larger axial dimension compared with a vane pump or a geared pump owing to the screw spindles. As a result, the use of screw pumps as oil pumps is known predominantly for supplying lubrication oil to large-volume combustion engines in ships or even lorries in which more installation space is available and the combustion engine is operated at a relatively constant rotational speeds.

If a screw pump is used in the application as an oil pump, the delivery pressure may exceed the permissible operating range of the oil pressure in the combustion engine during rapid rotational speed increases or high rotational speeds. In said applications in ships or lorries, e.g. the delivery volume of the screw pump is adjusted in that some of the delivery volume recirculates through an adjustable bypass from an outlet back to an inlet of the screw pump and runs through the spindle chamber once again, whereby the resulting delivery flow in the lubrication oil delivery system is reduced. For instance, DE 10 2009 056 218 A1 describes a screw pump on which a pressure-limiting valve with a return path is integrated, whereby, above a set delivery pressure, a hydraulic short-circuit is produced between the pressure side and suction side of the pump. However, the response behaviour of such an adjustment is relatively slow and appears to be unsuitable in view of the rapid rotational speed fluctuations during operation of internal combustion engines in passenger cars.

Patent application DE 10 2018 109 886.9 which was not yet published on the filing date of the present invention and is by the same applicant proposes an adjustable lubrication oil delivery system for combustion engines in utility vehicles having an improved response behaviour, in which suction throttling occurs upstream of the screw pump. In the system, a pressure of the lubrication oil downstream of the throttle valve and upstream of a pump inlet is lowered to the negative pressure of the suction side of the pump chamber or the spindle chamber, whereby a pressure difference—which is necessary for filling the spindle chamber within a rotational speed-dependent time—is not achieved. DE 10 2018 109 886.9 deals with the principle of suction throttling and an implementation of the system in terms of control technology, without addressing a specific design of the screw pump or the upstream throttle valve in terms of the application in utility vehicles or lorries.

As explained above, there is a need for an efficient screw pump which is suitable for use as an oil pump in a passenger car. Accordingly, an object of the present invention is to provide a compact design for a screw pump and an adjustment of the delivery amount.

The object is achieved by a controllable or an adjustable screw pump having the features of claim 1.

The controllable screw pump is characterised in particular in that, inside the pump housing, a throttle chamber and a control chamber are provided, which are in contact with the lubrication oil to be conveyed, wherein the throttle chamber is situated between the pump inlet and the spindle chamber, and the throttle chamber includes a throttle valve, via which a flow cross-section of a delivery flow is settable; the control chamber includes a hydraulic regulating valve with a piston that responds to a hydraulic control pressure inside the control chamber, and the control chamber is arranged in parallel to the spindle chamber with reference to a displacement of the piston; and a valve body of the throttle valve is coupled with the piston of the hydraulic regulating valve.

The invention thus provides for the first time an integrated design of a screw pump and a hydraulically controlled suction throttling.

The compact design of the controllable or adjustable screw pump offers a solution for the need to have a considerably more efficient supply of lubrication oil in passenger cars. In so doing, the robust basic design of the screw pump with the advantages of the high degree of efficiency, robustness and low pulsation over other displacement pumps is retained.

By integrating the suction throttling in the pump housing, the installation space and the installation of a component in the lubrication oil system can be omitted. An assembly is produced which is comparable to the known types of variable pumps with variable geometry.

The arrangement of the hydraulic regulating valve in parallel to the screw spindles allows a similar bounding geometry of the pump housing, in which—despite the integration of the suction throttling—the axial dimension remains substantially unchanged and a radial dimension is increased to an insignificant extent. Therefore, the optimisation of an installation space in new systems or a replacement of the pump in current applications with a predetermined installation space is facilitated.

The hydraulic implementation permits a higher power density in relation to the actuating force for setting the suction throttling, and so the hydraulic regulating valve can be smaller compared with electric actuating members or the like and more installation space is saved.

A high adjusting dynamic is achieved by the integrated design. The invention is based on the knowledge that, during suction throttling, down time between regulating engagement and step response is in relation to the throttled suction path. As a result of the short distance between the throttle valve and the spindle chamber, the delivery amount can be changed in a highly dynamic manner.

Advantageous developments of the adjustable lubrication oil delivery system are the subject matter of the dependent claims.

According to one aspect of the invention, a displacement of the valve body of the throttle valve can be arranged in parallel to the spindle chamber, and a valve seat of the throttle valve can be provided at a mouth of the pump inlet into the throttle chamber. Therefore, the hydraulic regulating valve and also the throttle valve are arranged in parallel to the spindle chamber, thus favouring a compact design of the pump structure.

According to one aspect of the invention, the valve body of the throttle valve and the piston of the hydraulic regulating valve can be seated on a common valve stem. Therefore, there is no need to separately guide the valve body of the throttle valve and the integrated formation of both valves favours the compact design of the pump structure.

According to one aspect of the invention, the screw pump can comprise two screw spindles, wherein a cross-section of the spindle chamber is formed by two overlapping circle radii, and a cross-section of the control chamber can be situated in the area of an intersection axis of an overlap of the circle radii next to the spindle chamber. By way of this formation, the overall radial dimension can be reduced, thus favouring the compact design of the screw pump.

According to one aspect of the invention, the control chamber can comprise two hydraulic connections for introducing two hydraulic control pressures that act on opposing sides of the piston of the hydraulic regulating valve. Therefore, in addition to one variant of a hydraulic regulating valve in which a control pressure acts against a spring bias, another variant in relation to the hydraulic actuation is provided which is less critical in terms of sealing the piston.

According to one aspect of the invention, a compression spring can be situated inside the control chamber on one side of the piston of the hydraulic regulating valve. A compression spring can be used to provide a fail-safe function, and so a suction throttling can be set to a predetermined or complete opening position of the valve element in the case of a loss in control pressure owing to a failure in the hydraulic actuation.

According to one aspect of the invention, the pump housing can comprise at one end face of the spindle chamber a collar portion that includes a passage for the housing and a shaft bearing for a drive shaft, and a gear rim that is seated on the drive shaft can comprise a radial cut-out for the collar portion so that a toothing of the gear rim and the shaft bearing overlap axially. By way of this formation, the overall axial dimension can be reduced, thus favouring the compact design of the screw pump.

The invention will be explained hereinafter with the aid of an embodiment and with reference to the accompanying drawing,

FIG. 1 shows a simplified schematic sectional view through the design of one embodiment of the controllable screw pump in accordance with the invention.

In the embodiment of the schematic illustration of FIG. 1, a relative dimension of a hydraulic regulating valve 4 has been selected in favour of improved perception.

However, the hydraulic regulating valve 4 can likewise be smaller. Furthermore, to avoid a superimposed illustration of the hydraulic regulating valve 4 with a spindle chamber 12, in FIG. 1 a position of the hydraulic regulating valve 4 is shown offset with respect to the spindle chamber 12. However, a position and distance of the hydraulic regulating valve 4 with respect to the spindle chamber 12 can likewise vary in favour of a more compact arrangement.

In terms of this disclosure, the term ‘screw pump’ is understood to mean skew rotary piston pumps with a thread pitch for displacement of the delivery medium. Such types of pump generally comprise a driven screw spindle 2 a and at least one further screw spindle 2 b which is dragged via engagement of the toothing.

The screw pump of the illustrated embodiment has one driven screw spindle 2 a and one dragged screw spindle 2 b which are rotatably accommodated in a spindle chamber 12 of a pump housing 10. The driven screw spindle 2 a communicates with a drive shaft 5 which is driven by a combustion engine via a gear rim 50. The drive shaft 5 exits the pump housing 1 in a collar portion 15. A shaft bearing 51 in the form of a compact bearing having two rows of ball bearings is fitted in the collar portion 15. The gear rim 50 is seated on the free end of the drive shaft 5, protruding therefrom, and has a bulge for the collar portion 15, and so a radial outer toothing axially overlaps with the shaft bearing 51.

A pressure side of the spindle chamber 12 which communicates with a pump outlet 11 in the form of a pressure connection is located on the drive side of the screw spindles 2 a, 2 b. A suction side of the spindle chamber 12 is located on the side of the screw spindles 2 a, 2 b opposite the drive. The suction side of the spindle chamber 12 communicates with a pump inlet 10 in the form of a suction connection via a throttle chamber 3. In consideration of the delivery direction, lubrication oil is sucked through by a negative pressure on the suction side of the spindle chamber 12, which is generated by a screw pitch of the rotating screw spindles 2 a, 2 b, via the pump inlet 10 and the throttle chamber 3, is conveyed through the spindle chamber 12 and ejected out of the spindle chamber 12 on the pressure side via the pump outlet 11.

A suction path upstream of the screw pump leads to an oil sump of the combustion engine. Downstream of the screw pump, a feed path of a lubrication oil delivery system, not illustrated, is provided. The feed path leads to branches of a lubrication oil supply of the combustion engine which serves to lubricate sliding surfaces between moving parts in a crank drive, a valve drive and cylinder barrels and the like under a required oil pressure.

The throttle chamber 13 of the pump housing 1 forms an inlet chamber at an end face of the spindle chamber 12. An annular valve seat 31 of a throttle valve 3 is formed at a mouth, at which the suction connection of the pump inlet 10 enters the throttle chamber 3. A valve body 30 of the throttle valve 3 is guided at a valve stem 34 axially opposite the suction connection of the pump inlet 10 and has a spherical sealing surface. By way of an opening position along a displacement of the valve body 30 with respect to the valve seat 31, a flow cross-section of the delivery flow of the lubrication oil between the pump inlet 10 and the spindle chamber 12 is set or limited, whereby a suction throttling of the screw pump is performed. On the other side of the valve stem 34 opposite the valve body 30, there is arranged a piston 40 which is accommodated in a cylindrical control chamber 14 of the pump housing 1. The piston 40 and the control chamber 14 form a hydraulic regulating valve 4 which sets an opening position of the throttle valve 3 by a controlled supply of pressure of the lubrication oil.

The spindle chamber 12 has a cross-sectional contour in the form of a so-called Figure-of-eight housing, i.e. it is formed by two bores in the pump housing 1 with overlapping radii in order to ensure engagement of the screw spindles 2 a, 2 b. The cylindrical control chamber 14 of the hydraulic regulating valve 4 is likewise formed by a bore in the pump housing 1 which extends in parallel to the bores of the spindle chamber 12. In a preferred compact embodiment which differs from the schematic illustration in FIG. 1, the cylindrical control chamber 14 is arranged close to a bulge of the Figure-of-eight housing, i.e. between the axes of the bores of the spindle chamber 12 close to a chamber wall of the spindle chamber 12, and so a tight packing of cylindrical cavities and thus a compact bounding geometry of the pump housing 1 is created.

The integrated arrangement of the hydraulic regulating valve 4 and of the throttle valve 3 is separated by a common stem guide 43 which is formed between the control chamber 14 and the throttle chamber 13. The stem guide 43 provides an axial guide for the common valve stem 34. A position of the piston 40 along a displacement of the hydraulic regulating valve 4 is set by two hydraulic control pressures p1 and p2 which prevail on both sides of the piston 40 in the control chamber 14. The control pressure p1 is generated via a hydraulic connection 41 on one side of the piston 40 in the control chamber 14. The control pressure p2 is generated via a hydraulic connection 42 on the other side of the piston 40 in the control chamber 14. An actuating movement of the piston 40 is responsive to a pressure difference between the two control pressures p1, p2 and retains a position in the event of an equilibrium of forces on both sides of the piston 40.

On the side of the control pressure p1, a compression spring, not shown, is preferably arranged which intervenes in the force ratio of the control pressures p1, p2. The length of the compression spring is selected such that without the two control pressures p1, p2 a closed position of the throttle valve 3 is prevented. The use of a compression spring ensures a fail-safe function, and so in the event of a failure in the hydraulic adjustment, stopping of the lubrication oil supply whilst the combustion engine is running is prevented by a closed throttle valve 3. Likewise, a complete opening position of the throttle valve 3 can optionally be prevented by a further compression spring on the opposite side. Depending upon the configuration of the lubrication oil system, a critical delivery pressure will not be exceeded in the event of a failure in the hydraulic adjustment.

A hydraulic actuation of the two control pressures p1, p2 occurs in a lubrication oil system, not illustrated, via an electric-hydraulic regulating device which is fed from the lubrication oil circuit of the combustion engine and by the delivery pressure of the screw pump. Such an electric-hydraulic regulating device has an electromagnetic 4/3 proportional valve. The 4/3 proportional valve comprises four connections, including an input connection for the supply of oil from an oil gate of the combustion engine and three output connections, two output connections of which provide the two control pressures p1, p2 with a controlled pressure difference and one output connection of which returns oil having an excess differential pressure from the adjustment into the oil sump. The output connections of the two control pressures p1, p2 are adjusted by means of a valve body which sets a respective hydraulic resistance and thus a respective pressure difference between the input connection and the three output connections. The valve body is adjusted by an electromagnetic actuating member having a coil and an anchor, and by a compression spring. The electromagnetic actuating member is actuated by a pulse width modulation of a supplied electrical power. A control of the control pressures p1, p2 of the hydraulic regulating valve 4 for adjusting the delivery volume of a lubrication oil circuit via the suction throttling of the throttle valve 3 in the screw pump can be effected by a control device in dependence upon a load, a rotational speed and a temperature of the combustion engine.

LIST OF REFERENCE NUMERALS

-   1 Pump housing -   2 a Driven screw spindle -   2 b Dragged screw spindle -   3 Throttle valve -   4 Hydraulic regulating valve -   5 Drive shaft -   10 Pump inlet -   11 Pump outlet -   12 Spindle chamber -   13 Throttle chamber -   14 Control chamber -   15 Collar portion -   30 Valve body -   31 Valve seat -   34 Valve stem -   40 Piston -   41 Hydraulic connection with control pressure p1 -   42 Hydraulic connection with control pressure p2 -   43 Stem guide -   50 Gear rim -   51 Shaft bearing 

1-7. (canceled)
 8. A controllable screw pump for supplying lubrication oil to a combustion engine, comprising: a pump housing with a spindle chamber as well as a pump inlet and a pump outlet communicating with the spindle chamber; at least two screw spindles rotatably accommodated in the spindle chamber, the screw spindles being driven by the combustion engine; wherein inside the pump housing, a throttle chamber and a control chamber are provided, which are in contact with the lubrication oil to be conveyed; wherein the throttle chamber is situated between the pump inlet and the spindle chamber, and the throttle chamber includes a throttle valve, via which a flow cross-section of a delivery flow is settable; the control chamber includes a hydraulic regulating valve with a piston that responds to a hydraulic control pressure inside the control chamber, and the control chamber is arranged in parallel to the spindle chamber with reference to a displacement of the piston; and a valve body of the throttle valve is coupled with the piston of the hydraulic regulating valve.
 9. The controllable screw pump according to claim 8, wherein a displacement of the valve body of the throttle valve is arranged in parallel to the spindle chamber, and a valve seat of the throttle valve is provided at a mouth of the pump inlet into the throttle chamber.
 10. The controllable screw pump according to claim 8, wherein the valve body of the throttle valve and the piston of the hydraulic regulating valve are seated on a common valve stem.
 11. The controllable screw pump according to claim 8, wherein the screw pump comprises two screw spindles, wherein a cross-section of the spindle chamber is formed by two overlapping circle radii, and a cross-section of the control chamber is situated in the area of an intersection axis of an overlap of the circle radii next to the spindle chamber.
 12. The controllable screw pump according to claim 8, wherein the control chamber comprises two hydraulic connections for introducing two hydraulic control pressures that act on opposing sides of the piston of the hydraulic regulating valve.
 13. The controllable screw pump according to claim 8, wherein a compression spring is situated inside the control chamber on one side of the piston of the hydraulic regulating valve.
 14. The controllable screw pump according to claim 8, wherein the pump housing comprises at one end face of the spindle chamber a collar portion that includes a passage for the housing and a shaft bearing for a drive shaft, and a gear rim that is seated on the drive shaft comprises a radial cut-out for the collar portion so that a toothing of the gear rim and the shaft bearing overlap axially. 